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In early November, in both the Northern and the Southern Hemispheres, the constellation Orion the Mighty Hunter rises into the evening sky at about 10 p.m. local time. In both hemispheres, you'll see him just above the eastern horizon. Orion's stars (or all the stars for that matter) return to the same place in the sky about four minutes earlier with each passing night, or about one half hour earlier with every passing week.
If you live in the Northern Hemisphere, the W or M-shaped constellation Cassiopeia the Queen announces the hour of Orion's arrival better than any mechanical clock. At early evening, you'll see Cassiopeia in your northeast sky, to the right -- or upper right -- of Polaris, the north star. As evening progresses, Cassiopeia rotates counter-clockwise around Polaris and reaches upper transit over the north star -- her twelve o'clock position in the sky -- at the same time that Orion appears over your eastern horizon.
Meanwhile, in the the Southern Hemisphere, Orion the Mighty Hunter always appears over the eastern horizon as the constellation Crux (the Southern Cross) sinks to it lowest point in the sky. In other words, when Orion rises above the eastern horizon, Cassiopeia climbs to her highest elevation in the northern skies, while Crux (or the Southern Cross) descends to its nadir in the southern skies.
In fact, anyplace north of 25 degrees SOUTH latitude (the latitude of middle Australia and northern South Africa) can't even see the Southern Cross when Orion first appears in the east, because it's beneath the horizon at this time. But as you look due north from 25 degrees south latitude (assuming an unobstructed view), you can see Cassiopeia just above the horizon. That's because Cassiopeia and Crux are mutually exclusive constellations. Worldwide, as one of these constellations exits the sky, the other one enters the sky. One always rises about-face from where the other one sets.
One half year from now -- at about 10 p.m. local time in early May -- everything will be reversed. Orion will have sunk beneath the western horizon -- at which time, Cassiopeia will be at lower transit and Crux at upper transit. The tropical and subtropical regions of the Northern Hemisphere (anywhere south of 25 degrees NORTH latitude) will see that Crux has bumped Cassiopeia from the evening sky.
Keep in mind that if you live in a region of the globe where one of these two constellations is circumpolar (in the sky all year long), then the other constellation will never appear in your sky. Cassiopeia is circumpolar anywhere north of 35 degrees N. latitude, and Crux is circumpolar anywhere south of 35 degrees S. latitude. At 30 degrees latitude, south or north, one of these constellations half rises as the other constellation half sets, essentially removing both constellations from the sky.
Queen Cassiopeia, whose vanity is the stuff of legend, wants you to know that the upcoming cold season in the Northern Hemsiphere elevates the impeccably beautiful Queen to her moment of glory. If you're blessed with a clear, dark night, you'll see her sitting atop the the Milky Way -- the luminous band of stars (or is it hoarfrost?) arching from east to west across the sky.
Whereas Cassiopeia's throne reigns at the northern terminus of the Milky Way, the Milky Way's southern terminus is the dominion the constellations Crux and Musca the Fly.
copyright 2004 by Bruce McClure
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